This invention relates to integrated circuits, and more particularly, to circuitry and design systems for integrated circuits that can be used to improve performance and reduce power consumption by making transistor power supply and body bias adjustments.
There is an ongoing effort in the semiconductor industry to improve device performance. Improvements in speed, power consumption, and density have been achieved by scaling down transistor components to smaller sizes and lower operating voltages. Part of these scaling efforts have resulted in reduced values of transistor threshold voltage. Low transistor threshold voltages are generally advantageous, because they help to improve transistor switching speed. However, low transistor threshold voltages may also lead to increased transistor leakage currents. Elevated levels of transistor leakage are undesirable, because transistor leakage can produce undesired power losses.
To ensure that transistor leakage currents do not become excessive as threshold voltages are scaled to lower values, some integrated circuits are operated with reduced power supply voltages. For example, the positive power supply voltage that is used to power an integrated circuit's core logic may be reduced from 1.5 volts to 1.2 volts in an attempt to compensate for the leakage current increases that are produced from threshold voltage reductions. Although reductions in power supply voltages can be helpful in reducing power consumption, power supply voltages cannot be reduced too much without adversely affecting transistor switching speeds.
To address these issues, some integrated circuit designs use body biasing arrangements in which the bulk or body terminals of certain transistors in the circuit are biased to increase the transistors' threshold voltage. Transistors with body terminals that are biased in this way exhibit reduced leakage. Power can also be conserved by placing portions of a circuit that are not being used into a sleep state by removing their positive power supply voltage.
Although techniques such as these help to reduce power consumption while preserving device performance, it is not always possible to bias the body terminal of transistors in active circuits, because body bias arrangements reduce transistor speed. Moreover, transistors that form part of an active circuit cannot be placed in a sleep state, because the circuit will not function in its sleep state.
It would therefore be desirable to be able to provide improved ways in which to address transistor performance and power consumption challenges for integrated circuits.